The present invention relates to apparatus for making cigarettes or analogous rod-shaped articles of the tobacco processing industry, and more particularly to improvements in the making of cigarettes, cigars or cigarillos with so-called dense ends. The following description of the invention will deal primarily with the making of cigarettes but the same procedure can be followed in connection with the making of other rod-shaped articles of the tobacco processing industry. Such articles are intended to embrace those which contain smokable material as well as those which contain filter material for tobacco smoke.
Cigarettes are made in so-called rod making machines wherein a continuous shower of fibrous material (such as particles of natural tobacco leaves, fragments of sheets of reconstituted tobacco and/or fragments of substitute tobacco) is attracted to one side of an air-permeable belt conveyor which accumulates a continuous stream containing a surplus of fibrous material. The surplus is removed by a trimming or equalizing device, and the resulting trimmed stream or filler is thereupon draped into a continuous web of cigarette paper or other suitable wrapping material to form therewith a continuous cigarette rod which is subdivided into sections of unit length or multiple unit length. Such sections can be admitted into a filter tipping machine, into a packing machine or to storage. A suction chamber at the other side of the air-permeable conveyor attracts the shower of fibrous material and thereupon the built up stream during travel toward, past and beyond the surplus removing station.
It is already known to densify longitudinally spaced-apart portions of the continuous stream so as to establish zones of greater density. If the cigarette rod is severed across or adjacent such zones of greater density, each of the thus obtained cigarettes will have one or two dense ends. The purpose of densifying one or both ends of each cigarette is to reduce the likelihood of escape of fragments of tobacco.
Densification of selected portions of a continuous stream of tobacco or similar fibrous material is normally effected by removing less tobacco from those portions of the stream which are to constitute the filler portions at the ends of cigarettes. In accordance with a presently known proposal, the removal of surplus at the trimming station is regulated by employing specially designed trimming discs the peripheries of which are provided with pockets so that the discs remove more tobacco from spaced-apart first portions of the advancing stream and less tobacco from second portions of the same stream which alternate with the first portions.
In accordance with a different proposal which is disclosed in British Pat. No. 948,736, the conveyor for the continuous tobacco stream is a circulating wheel with a circumferential groove in which the stream advances past the trimming station. The groove is adjacent a suction chamber including portions which attract the fibrous material with a greater force in those regions where the cigarette ends should contain more tobacco. A similar apparatus is disclosed in U.S. Pat. No. 3,306,305 which describes an apparatus employing an air-permeable conveyor in the form of a metallic band having openings for the passage of air streams. The combined cross-sectional area of openings in first sections of the band deviates from the combined cross sectional area of openings in second sections which alternate with the first sections. This enables the conveyor to attract different portions of the stream with a different force and such treatment of tobacco also results in the making of a stream which is ready for conversion into the filler of a cigarette rod capable of being subdivided into cigarettes with dense ends.
A drawback of the patented apparatus is that the stream is likely to slip relative to the wheel-shaped or metallic band-like conveyor with the resulting displacement of densified zones. Another drawback of the patented apparatus is that a different wheel and a different steel band is necessary for each type of cigarettes, namely for shorter, medium long and longer cigarettes. Consequently, each change of setup takes up a substantial amount of time and the machine utilizing such apparatus must be furnished with a number of spare conveyors.